Not Applicable
Not Applicable
1. Field of the Invention
The field of the present invention is digital cross-connect systems. More particularly, the invention relates to protection switching in a digital cross-connect system signal processing unit.
2. Description of the Prior Art
Digital cross-connect systems are used in digital networks to make interconnections between multiple signal carrying links at the channel level. Such systems conventionally include a Main Controller (MC) and at least one signal processing unit adapted to perform multiplexing, demultiplexing and interworking of incoming signal traffic. The signals may be formatted according to traffic protocols such as SDH (Synchronous Digital Hierarchy), SONET (Synchronous Optical Network), or PDH (Pleisochronous Digital Hierarchy). As is well known in the art, the signal processing unit includes various digital signal processing devices, typically embodied as circuit packs, that perform the required functions. These devices may include link interfaces, mappers, formatters and cross-connect networks. A Unit Controller (UC) typically implements local control functions in the signal processing unit under authority of the MC.
To improve system reliability, multiple copies of each signal processing device can be incorporated in a signal processing unit to provide device redundancy. One or more copies of each signal processing device can act as xe2x80x9cprotectionxe2x80x9d devices for the remaining copies of the device, which are known as xe2x80x9cservicexe2x80x9d devices and which represent a xe2x80x9cfailure group.xe2x80x9d A Protection SWitch (PSW) provides a control mechanism for switching between a service device and a protection device. This switching can be performed in response to both manual provisioning commands from a system administrator and autonomous requests generated as a result of hardware errors or network (facility) problems. In prior art digital cross-connect systems, all PSW requests, whether they are manual or autonomous in nature, are processed by the MC, which maintains a system-wide PSW database containing all system state information, including the identity of the active signal processing devices of each signal processing unit in the digital cross-connect system. The UC also maintains a local PSW database that identifies the active signal processing devices that it directly oversees. These databases must be coordinated in order for PSW processing to work effectively.
When the MC receives a provisioning command, it sends a corresponding PSW request to a UC, which implements the PSW operation. The PSW databases in the MC and the UC must then be updated to reflect the change of active signal processing devices. A different protection switch procedure is used when hardware error recovery processing is invoked or when network problems arise. In those cases, the device being affected by the hardware error or network problem first notifies the responsible UC, which performs a xe2x80x9cfast switchxe2x80x9d PSW operation. A fast switch is a PSW operation performed without MC involvement in the switch decision making process. After the fast switch is performed, the UC sends a message to the MC advising it of the fast switch and requesting the MC to lock its PSW database. After locking the database, the MC forwards a PSW request to the UC to perform a normal xe2x80x9cslow switchxe2x80x9d PSW operation. A slow switch is a PSW operation performed at the request of the MC. After the slow switch is performed, the MC updates and synchronizes both the MC and the UC databases.
It will be seen that the error recovery scenario described above requires duplicative PSW actions. Moreover, a potential race condition and deadlock situation may result from the UC having to serve both fast switch and slow switch PSW requests. Accordingly, there is a need in the digital cross-connect system art for a protection switch that does not suffer from these disadvantages. What is required is a protection switch architecture that implements both manual and autonomous PSW commands without redundant processing and the inherent difficulties of fast and slow PSW switching.
The foregoing problems are solved and an advance in the art is obtained by a novel protection switch architecture for a digital cross-connect system of the type which has a main controller, a command interface, and at least one digital signal processing unit. The digital signal processing unit includes one or more signal processing service devices and one or more signal processing protection devices that correspond to the service devices. A unit controller includes the new protection switch of the invention for switching signal processing responsibilities between the service devices and the protection devices. Advantageously, the protection switch is adapted to act independently of the main controller in response to autonomous protection requests from the service devices by completing all protection switching related to such protection requests without main controller involvement. The protection switch also acts in response to manual switching requests from the main controller.
In preferred embodiments of the invention, protection switch control functions are implemented in an object oriented software environment by a protection manager object, one or more service objects associated with the service devices, and one or more protection objects associated with the protection devices. The foregoing objects each preferably include a main controller half-object residing in the main controller and a unit controller half-object residing in the unit controller. Other half-objects, representing signal link facility objects, may be distributed between the unit controller and processors in the service and protection devices.